I thought I would share my idea of changing back footstrap positions and a bit of reinforcement/safety for the tuttle box.
I found the outboard position of the back straps almost impossible to use, I made this up and thought it would be just a temp measure but may keep it as it is.
Cool, let us know how it holds up. I too am using a formula board and foil and have found it alright in the back outboard strap when there is enough wind. I think most of it is getting outboard to get leverage over the rig. You see those guys cooking on wide formulas in the outboard straps.
I understand your line of thinking. It seemed impossible to utilize the back straps on my setup, the outboard positioning just didn't seem right. I'm finally in the back straps in their outboard position. Here were my mistakes.
1. Position (Stand upright): When learning, I was trying to attack the wind much like a traditional windsurfer... leaning over and weighting in the heals. This led to multiple failures. You need to stand further upright, even when in the rear footstrap. Remember to lock out your rear foot/heal to keep the board steady.
2. Wind strength & angle: There was a video done here in the US that discusses the idea of not using rear straps at all for a while.